4 research outputs found
Packet dropping characteristics in a queue with autocorrelated arrivals
This paper provides a detailed description of the packet dropping process connected with the buffer overflows in a network node. Namely, we show the formulas for the most important loss characteristics, both in the transient and the stationary regime and then illustrate them via numericalexamples. In order to make it possible to obtain the droppingcharacteristics for strongly autocorrelated arrivals, the Markovmodulated Poisson process is used as a traffic model
Unreliable Retrial Queues in a Random Environment
This dissertation investigates stability conditions and approximate steady-state performance measures for unreliable, single-server retrial queues operating in a randomly evolving environment. In such systems, arriving customers that find the server busy or failed join a retrial queue from which they attempt to regain access to the server at random intervals. Such models are useful for the performance evaluation of communications and computer networks which are characterized by time-varying arrival, service and failure rates. To model this time-varying behavior, we study systems whose parameters are modulated by a finite Markov process. Two distinct cases are analyzed. The first considers systems with Markov-modulated arrival, service, retrial, failure and repair rates assuming all interevent and service times are exponentially distributed. The joint process of the orbit size, environment state, and server status is shown to be a tri-layered, level-dependent quasi-birth-and-death (LDQBD) process, and we provide a necessary and sufficient condition for the positive recurrence of LDQBDs using classical techniques. Moreover, we apply efficient numerical algorithms, designed to exploit the matrix-geometric structure of the model, to compute the approximate steady-state orbit size distribution and mean congestion and delay measures. The second case assumes that customers bring generally distributed service requirements while all other processes are identical to the first case. We show that the joint process of orbit size, environment state and server status is a level-dependent, M/G/1-type stochastic process. By employing regenerative theory, and exploiting the M/G/1-type structure, we derive a necessary and sufficient condition for stability of the system. Finally, for the exponential model, we illustrate how the main results may be used to simultaneously select mean time customers spend in orbit, subject to bound and stability constraints
On the distribution of throughput of transfer lines
Ankara : Department of Industrial Engineering and the Institute of Engineering and Sciences of Bilkent University, 1998.Thesis (Master's) -- Bilkent University, 1998.Includes bibliographical references leaves 86-107A transfer line corresponds to a manufacturing system consisting of a number
of work stations in series integrated into one system by a common transfer
mechanism and a control system. There is a vast literature on the transfer
lines. However, little has been done on the transient analysis of these systems
by making use of the higher order moments of their performance measures
due to the difficulty in determining the evolution of the stochastic processes
under consideration. This thesis examines the transient behavior of relatively
short transfer lines and derives the distribution of the performance measures
of interest. The proposed method based on the analytical derivation of the
distribution of throughput is also applied to the systems with two-part types.
An experiment is designed in order to compare the results of this study with the
state-space representations and the simulation. They are also interpreted from
the point of view of the line behavior and design issue. Furthermore, extensions
are briefly discussed and directions for future research are suggested.Deler, BaharM.S